Quantum dot solar cell

ABSTRACT

A solar cell including a quantum dot and an electron conductor, with a bifunctional ligand disposed between the quantum dot and the electron conductor. The bifunctional ligand molecule may include an electron conductor anchor that bonds to the electron conductor and a first quantum dot anchor that bonds to the quantum dot. A hole conductor such as a conductive polymer may include a second quantum dot anchor. In some instances, the first quantum dot may include selenium.

PRIORITY

This application claims priority under 35 U.S.C. §119 to U.S. Provisional Application Ser. No. 61/047,015 entitled “QUANTUM DOT SOLAR CELL” filed Apr. 22, 2008, the entirety of which is incorporated herein by reference.

TECHNICAL FIELD

The disclosure pertains generally to solar cells and more particularly to quantum dot solar cells.

SUMMARY

The disclosure pertains generally to solar cells. In some instances, a solar cell may include quantum dots. In an illustrative but non-limiting example, the disclosure pertains to a solar cell that includes an electron conductor layer, a quantum dot layer and a bifunctional ligand layer that is coupled to the electron conductor layer and to the quantum dot layer. The bifunctional ligand layer may include selenium. A hole conductor layer is also coupled to the quantum dot layer.

In another illustrative but non-limiting example, the disclosure pertains to a solar cell that includes an electron conductor, a quantum dot and a selenium-based bifunctional ligand that is coupled between the electron conductor and the quantum dot. A hole conductor including a sulfur-functionalized thiophene is also coupled to the quantum dot.

In another illustrative but non-limiting example, the disclosure pertains to a solar cell that includes an electron conductor and a quantum dot. A bifunctional ligand may have an electron conductor anchor secured to the electron conductor as well as a selenium-based quantum dot anchor that is secured to the quantum dot. A sulfur-based hole conductor may also be secured to the quantum dot.

The above summary is not intended to describe each disclosed embodiment or every implementation of the disclosure. The Detailed Description which follow more particularly exemplify these embodiments.

BRIEF DESCRIPTION OF THE FIGURES

The following description should be read with reference to the drawings. The drawings, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of the disclosure. The disclosure may be more completely understood in consideration of the following detailed description of various embodiments in connection with the accompanying drawings, in which:

FIG. 1 is a schematic cross-sectional side view of an illustrative but non-limiting example of a solar cell; and

FIG. 2 is a schematic cross-sectional side view of another illustrative but non-limiting example of a solar cell.

While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

DETAILED DESCRIPTION

The following description should be read with reference to the drawings, in which like elements in different drawings are numbered in like fashion. The drawings, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of the invention. Although examples of construction, dimensions, and materials are illustrated for the various elements, those skilled in the art will recognize that many of the examples provided have suitable alternatives that may be utilized.

FIG. 1 is a schematic cross-sectional side view of an illustrative solar cell 10. In the illustrative example shown in FIG. 1, there may be a three-dimensional intermingling or interpenetration of the layers forming solar cell 10, but this is not required. The illustrative solar cell 10 includes a quantum dot layer 12. Quantum dot layer 12 may schematically represent a single quantum dot. In some cases, quantum dot layer 12 may be considered as representing a large number of individual quantum dots.

In the illustrative embodiment of FIG. 1, a bifunctional ligand layer 14 is provided, and may schematically represent a single bifunctional ligand, such as those discussed below. In some cases, bifunctional ligand layer 14 may represent a large number of individual bifunctional ligands, with at least some of the bifunctional ligands within bifunctional ligand layer 14 bonded to corresponding quantum dots within quantum dot layer 12. The illustrative solar cell 10 of FIG. 1 also includes an electron conductor layer 16. In some cases, electron conductor layer 16 may be an n-type conductor as discussed below. The illustrative solar cell 10 may further include a hole conductor layer 18. As discussed below, hole conductor layer 18 may be a p-type conducting electrode layer.

Bifunctional ligand layer 14 may, in some instances, be considered as being coupled to quantum dot layer 12 as well as being coupled to electron conductor layer 16. Similarly, hole conductor layer 18 may also be considered as being coupled to quantum dot layer 12. In some cases, two layers may be considered as being coupled if one or more molecules or other moieties within one layer are bonded or otherwise secured to one or more molecules within another layer. In some instances, coupling infers the potential passage of electrons from one layer to the next.

Quantum dot layer 12 may include one quantum dot or a plurality of quantum dots. Quantum dots are typically very small semiconductors, having dimensions in the nanometer range. Because of their small size, quantum dots may exhibit quantum behavior that is distinct from what would otherwise be expected from a larger sample of the material. In some cases, quantum dots may be considered as being crystals composed of materials from Groups II-VI, III-V, or IV-VI materials. The quantum dots employed herein may be formed using any appropriate technique. Examples of specific pairs of materials for forming quantum dots include, but are not limited to, MgO, MgS, MgSe, MgTe, CaO, CaS, CaSe, CaTe, SrO, SrS, SrSe, SrTe, BaO, BaS, BaSe, BaTe, ZnO, ZnS, ZnSe, ZnTe, CdO, CdS, CdSe, CdTe, HgO, HgS, HgSe, HgTe, Al₂O₃, Al₂S₃, Al₂Se₃, Al₂Te₃, Ga₂O₃, Ga₂S₃, Ga₂Se₃, Ga₂Te₃, In₂O₃, In₂S₃, In₂Se₃, In₂Te₃, SiO₂, GeO₂, SnO₂, SnS, SnSe, SnTe, PbO, PbO₂, PbS, PbSe, PbTe, AlN, AlP, AlAs, AlSb, GaN, GaP, GaAs, GaSb, InN, InP, InAs and InSb.

FIG. 2 is a schematic cross-sectional side view of an illustrative solar cell 20 that is similar to solar cell 10 (FIG. 1). In some cases, a reflective and/or protecting layer 22 may be disposed over the hole conductor layer 18, as shown. The reflective and/or protecting layer 22 may be a conductive layer. In some instances, the reflective and/or protecting layer 22 may include a Pt/Au/C film as both catalyst and conductor, but this is not required. Alternatively, or in addition, a flexible and transparent substrate 24, shown at the lower side (in the illustrated orientation) of FIG. 2, may be an electron conductor such as an n-type electron conductor. The n-type electron conductor may be transparent or at least substantially transparent to at least some wavelengths of light within the visible portion of the electromagnetic spectrum.

As described with respect to FIG. 1, solar cell 10 may include a bifunctional ligand layer 14. In some cases, bifunctional ligand layer 14 may include a single bifunctional ligand or a large number of bifunctional ligands. A bifunctional ligand may, in some cases, be considered as improving electron transfer by reducing the energy barriers for electron transfer. A bifunctional ligand may provide a conduit so that electrons that are ejected by the quantum dot can travel to and through the electron conductor. A bifunctional ligand may, for example, secure the quantum dot relative to the electron conductor and/or any other related structure.

In some instances, a bifunctional ligand, such as may be included as part of bifunctional ligand layer 14 (FIG. 1), may be considered as including an electron conductor anchor that bonds to an electron conductor (such as electron conductor layer 16) as well as a quantum dot anchor that bonds to a quantum dot (such as a quantum dot within quantum dot layer 12). In some instances, the electron conductor anchor may include a carboxylic acid moiety. In some instances, the quantum dot anchor may include selenium.

In some instances, an appropriate selenium-based quantum dot anchor may be considered as being or otherwise including a moiety such as one of the following: —SeH and —SeR,

in which R is alkyl.

The term “alkyl” refers to a straight or branched chain monovalent hydrocarbon radical having a specified number of carbon atoms. Examples of “alkyl” include, but are not limited to, methyl, ethyl, n-propyl, isopropyl, n-butyl, s-butyl, t-butyl, n-pentyl, n-hexyl, 3-methylpentyl, and the like.

An illustrative but non-limiting example of a suitable bifunctional ligand is selenemethionine, which has the structure:

Another illustrative but non-limiting example of a suitable bifunctional ligand is selenohomocysteine, which has the structure:

Another illustrative but non-limiting example of a suitable bifunctional ligand is selenocystine, which has the structure:

Another illustrative but non-limiting example of a suitable bifunctional ligand is selenoglutathione, which has the structure:

Another illustrative but non-limiting example of a suitable bifunctional ligand is selenolipoic acid, which has the structure:

Another illustrative but non-limiting example of a suitable bifunctional ligand is seleno penicillamine, which has the structure:

Another illustrative but non-limiting example of a suitable bifunctional ligand is Se-methyl-selenocysteine, which has the structure

Another illustrative but non-limiting example of a suitable bifunctional ligand is selenoethionine, which has the structure:

Another illustrative but non-limiting example of a suitable bifunctional ligand is Se-allyl selenocysteine, which has the structure:

Another illustrative but non-limiting example of a suitable bifunctional ligand is Se-propyl selenocysteine, which has the structure:

It will be recognized that at least some of the bifunctional ligands described herein may include chiral carbons, and thus may include one or more stereoisomers. In some cases, a light sensitive assembly or a solar cell may include a single bifunctional ligand or a large number of bifunctional ligands. In some instances, the bifunctional ligand (if one) or at least some of the bifunctional ligands (if a plurality) may be dextrorotatory molecules. In some cases, the bifunctional ligand (if one) or at least some of the bifunctional ligands (if a plurality) may be levorotatory molecules. In some instances, at least some of a plurality of bifunctional ligands may include a racemic mixture of dextrorotatory molecules and levorotatory molecules.

In some instances, a solar cell that includes a large number of bifunctional ligands may include a large number of the same bifunctional ligand, each of which may be dextrorotatory molecules, levorotatory molecules or a racemic mixture thereof. In some cases, a light sensitive assembly or solar cell may include a large number of bifunctional ligands representing a plurality of different bifunctional ligands. Each group or subset of bifunctional ligands, either separately or in combination, may be dextrorotatory, levorotatory or a racemic mixture thereof.

Referring back to FIG. 1, the illustrative solar cell 10 may include an electron conductor layer 16, which may be formed of any suitable material. In some cases, the electron conductor layer 16 may be an n-type electron conductor. The electron conductor layer 16 may be metallic, such as TiO₂ or ZnO. In some cases, electron conductor layer 16 may be an electrically conducting polymer, such as a polymer that has been doped to be electrically conducting or to improve its electrical conductivity.

As discussed with respect to FIG. 1, the illustrative solar cell 10 may include a hole conductor layer 18 that is configured to reduce a quantum dot once the quantum dot has absorbed a photon and ejected an electron through the bifunctional ligand to the electron conductor. In some instances, the hole conductor may be a conductive polymer. In some cases, the conductive polymer may include a monomer that has an alkyl chain that terminates in a second quantum dot anchor. The conductive polymer may, for example, be or otherwise include a polythiophene that is functionalized with a moiety that bonds to quantum dots. In some cases, the polythiophene may be functionalized with a thio or thioether moiety.

An illustrative but non-limiting example of a suitable conductive polymer has

as a repeating unit, where R is absent or alkyl and m is an integer ranging from about 6 to about 12.

Another illustrative but non-limiting example of a suitable conductive polymer has

as a repeating unit, where R is absent or alkyl.

Another illustrative but non-limiting example of a suitable conductive polymer has

as a repeating unit, where R is absent or alkyl.

Another illustrative but non-limiting example of a suitable conductive polymer has

as a repeating unit, where R is absent or alkyl.

A solar cell may, for example, be assembled by growing nanoparticles of n-type semiconducting titanium dioxide on a glass substrate, optionally followed by a sintering process. Next, the quantum dots, the bifunctional ligands and the conducting polymer are synthesized. Finally, the solar cell may be assembled by combining the individual components in a one-pot synthesis.

The disclosure should not be considered limited to the particular examples described above, but rather should be understood to cover all aspects of the invention as set out in the attached claims. Various modifications, equivalent processes, as well as numerous structures to which the invention can be applicable will be readily apparent to those of skill in the art upon review of the instant specification. 

1. A solar cell comprising: an electron conductor layer; a quantum dot layer; a bifunctional ligand layer having an electron conductor anchor that bonds to the electron conductor layer and a quantum dot anchor that bonds to a quantum dot layer, the bifunctional ligand layer providing a conduit for electrons that are elected by the quantum dot to travel to the electron conductor layer, the bifunctional ligand layer including selenium; and a hole conductor layer coupled to the quantum dot layer.
 2. The solar cell of claim 1, wherein the bifunctional ligand layer comprises


3. The solar cell of claim 1, wherein the bifunctional ligand layer comprises


4. The solar cell of claim 1, wherein the bifunctional ligand layer comprises


5. The solar cell of claim 1, wherein the bifunctional ligand layer comprises


6. The solar cell of claim 1, wherein the bifunctional ligand layer comprises


7. The solar cell of claim 1, wherein the bifunctional ligand layer comprises


8. The solar cell of claim 1, wherein the bifunctional ligand layer comprises


9. The solar cell of claim 1, wherein the bifunctional ligand layer comprises


10. The solar cell of claim 1, wherein the bifunctional ligand layer comprises


11. The solar cell of claim 1, wherein the bifunctional ligand layer comprises


12. The solar cell of claim 1, wherein the hole conductor layer comprises a conductive polymer.
 13. The solar cell of claim 12, wherein the conductive polymer comprises

as a repeating unit, where R is absent or alkyl and m is an integer ranging from about 6 to about
 12. 